The invention relates to a method for blood pressure measurement, in which method a variable compressive acting pressure is applied to a measuring point, such as a person""s extremity or the like, at a compression point by a pressure generator, and at the same time the effect of the variable acting pressure on the artery is measured at a second point, the second point being located farther away from the heart, i.e. closer to the end point of peripheral circulation, than the compression point to which the acting pressure is applied, and in which method diastolic pressure is determined.
The invention also relates to a method for blood pressure measurement, in which method a variable compressive acting pressure is applied to a measuring point, such as a person""s extremity or the like, at a compression point by a pressure generator, and at the same time the effect of the variable acting pressure on the artery is measured at a second point, the second point being located farther away from the heart, i.e. closer to the end point of peripheral circulation, than the compression point to which the acting pressure is applied, and in which method systolic pressure is determined.
The invention further relates to an arrangement for blood pressure measurement, comprising a pressure generator for applying a compressive acting pressure to a measuring point, such as a person""s extremity or the like, the arrangement comprising an acting pressure measuring element, the arrangement further comprising an interpreting unit arranged to determine diastolic pressure, the arrangement comprising a sensor for simultaneous measurement of the effect of the variable acting pressure on an artery at a second point, said second point being farther away from the heart, i.e. closer to the end point of peripheral circulation, than the compression point to which the acting pressure is applied.
The invention also relates to an arrangement for blood pressure measurement, comprising a pressure generator for applying a compressive acting pressure to a measuring point, such as a person""s extremity or the like, the arrangement comprising an acting pressure measuring element, the arrangement further comprising an interpreting unit arranged to determine systolic pressure, the arrangement comprising a sensor for simultaneous measurement of the effect of the variable acting pressure on an artery at a second point, said second point being farther away from the heart, i.e. closer to the end point of peripheral circulation, than the compression point to which the acting pressure is applied.
The heart pumps and causes blood to flow in the blood vessels, arteries and veins. The pumping produces pressure in the blood, i.e. blood pressure. Blood pressure is particularly affected by heartbeat and the resistance provided by peripheral circulation. Psychic factors, medication, smoking and other factors, such as a person""s state, i.e. whether a person is asleep or awake, are also important.
The terms systolic pressure, diastolic pressure and venous pressure, are used when discussing blood pressure.
Technically, from the point of view of measurement, systolic pressure refers to the pressure at which an artery becomes blocked, i.e. heartbeat stops. Physiologically, systolic pressure refers to the maximum pressure generated by a pumping cycle of the heart.
Technically, from the point of view of measurement, diastolic pressure refers to the pressure at which heartbeat is resumed when the pressure pressing the artery is reduced. Physiologically, diastolic pressure refers to the minimum venous pressure value between two pumping cycles of the heart.
Venous pressure refers to the average pressure in a vein. At a certain stage of venous pressure measurement, a systolic and diastolic point can also be detected.
Blood pressure measurement is divided into two main categories: invasive, i.e. measurement from inside the body, and non-invasive, i.e. measurement from the outside of the body. The drawback in the invasive method is naturally that the measurement is made from inside a person""s body by the use of e.g. a catheter placed in an artery. The invasive method and the equipment solutions involved are unpleasant for a person, and the measurements involve much work and are cumbersome, since they require operating theatre conditions. A special drawback is the risk of infection and bleeding of the artery.
Currently two methods are known for non-invasive blood pressure measurement, i.e. measurement from outside of the body. These include the auscultatory measurement and the oscillometric measurement. The auscultatory method utilizes a stethoscope and an occluding cuff provided with a mercury manometer and a pressure pump, the cuff encircling a person""s extremity, such as the arm. The auscultatory method is based on auscultation of sounds known as the Korotkoff sounds by the stethoscope. The Korotkoff sounds are created by blood flowing in a partially occluded artery. In the auscultatory method the pressure of the occluding cuff, i.e. the acting pressure, is first raised above the estimated systolic pressure, whereby blood flow in the extremity being measured, such as the arm, is occluded. The pressure of the occluding cuff is then allowed to decline gradually, while the stethoscope is placed over the artery for auscultation on the distal side with respect to the occluding cuff. Once the pressure has been lowered sufficiently, snapping Korotkoff sounds can be detected by the stethoscope, and the current pressure is interpreted as the systolic pressure. Once the pressure of the occluding cuff is allowed to decline further, Korotkoff sounds are no longer heard, which means that the current pressure is the diastolic pressure at which the occluding cuff no longer occludes the artery. The drawback of the auscultatory method is its inaccuracy and that it requires an intent and experienced user.
Publication DE-2605528 teaches an application of the auscultatory method which additionally utilizes an optic pulse sensor disposed on the finger for following the variations in the pressure pulse. If the pressure pulse measured by the optic pulse sensor is observed to vary, this indicates a change in blood pressure from the previous measurement, and requires a new measurement. However, said procedure does not allow improvement of the accuracy and reliability of a single measurement, only that said information indicates the need for a repeat measurement.
Furthermore, a manual method based on palpation is known, in which pressure is produced by an occluding cuff in the arm, and a finger is used to palpate the pressure pulse of the radial artery, i.e. heartbeat. However, said method is inaccurate and unreliable.
Another widely used non-invasive method is the oscillometric measurement, in which an occluding cuff and the same principle are used, i.e. the acting pressure is first raised high, i.e. over the estimated systolic pressure, and then slowly declined, during which a pressure sensor comprised by the cuff is used to follow or observe the pressure oscillation signal of the cuff. Thus the essential difference as compared with the auscultatory method is that in the oscillometric method an electronic monitoring unit comprised by the device is used to follow the pressure oscillation measured by the pressure sensor inside the cuff instead of auscultation of an artery. As cuff pressure falls, the amplitude of the pressure oscillation in the cuff, i.e. the AC signal of the cuff pressure, increases to a certain pressure as the pressure is lowered, whereupon the oscillation decreases. When the pressure falls, oscillation, i.e. an AC-form pressure oscillation signal, or amplitude variation, is detectable in the cuff pressure. The amplitude of the pressure oscillation signal oscillation measured by the pressure sensor from the cuff reaches its maximum at a pressure known as mean arterial pressure. Systolic pressure can be measured relatively well by the oscillometric method, but diastolic pressure has to be calculated indirectly since the pressure oscillation signal oscillation measured by the cuff pressure sensor is still present at diastolic pressure, and hence indirect determination is used, in which the value of the diastolic pressure is the mean arterial pressure minus half of the difference between systolic and mean arterial pressure. A weakness of the oscillometric method is its inaccuracy and the resulting unreliability. Oscillometric devices and methods are technically simple, but this in turn results in the inability to monitor and observe the measurement and its reliability. The accuracy and reliability of oscillometric measurement have been improved by different signal processing methods by identifying different characteristics of the AC signal of the pressure pulse during measurement in association with determination of systolic and diastolic pressure. Publication U.S. Pat. No. 4,117,835, for example, discloses a method of monitoring the change in the AC signal derivative. However, in clinical measurements said methods have not been found to affect the accuracy.
A tonometric method, originally designed for ocular pressure measurement, has also been applied to blood pressure measurement. In the methods according to publication U.S. Pat. No. 5,033,471, the radial artery extending near a radius of the wrist is pressed. Since the surface resting against the sensor is even, intravenous pressure can be read at the middle sensor element. The method thus involves a direct non-invasive measurement. In principle the measurement is ideal and practical, but the skin causes a problem since it does not provide an ideal membrane between the sensor and the blood vessel. This is why calibration is required in tonometric methods, as described in e.g. publication U.S. Pat. No. 5,279,303.
It is an object of the present invention to provide a new kind of method and arrangement for blood pressure measurement, avoiding the problems of known solutions.
The object is achieved by a method according to the invention, characterized by transferring the measured value of the variable pressure acting on the measuring point at the compression point to such an interpreting unit to which is also applied the pressure pulse generated by the heart and measured by a sensor at said second point for determining the effect of the variable acting pressure, and by determining diastolic pressure in the interpreting unit on the basis of such an acting pressure which is measured by a measuring element and which is the acting pressure when the interpreting unit detects a sufficiently long-standing change in a pressure pulse signal measured by said sensor.
The object is achieved by a method according to the invention, characterized by transferring the measured value of the variable pressure acting on the measuring point at the compression point to such an interpreting unit to which is also applied the pressure pulse generated by the heart and measured by a sensor at said second point for determining the effect of the variable acting pressure, and by determining systolic pressure in the interpreting unit on the basis of such an acting pressure which is the acting pressure when the interpreting unit detects a sufficiently long-standing change in a pressure pulse signal measured by said sensor.
The measurement arrangement of the invention is characterized by using as the sensor for measuring the effect of the variable acting pressure at the second point said sensor which measures the pressure pulse generated by heartbeat and which is coupled to such an interpreting unit to which is also coupled a measured signal indicating the measured value of the acting pressure, and that the interpreting unit is arranged to determine diastolic pressure on the basis of such an acting pressure which is the pressure acting when the interpreting unit detects a change characteristic of diastolic pressure in a pressure pulse signal measured by the sensor which measures the artery.
The measurement arrangement of the invention is characterized by using as the sensor for measuring the effect of the variable acting pressure at the second point said sensor which measures the pressure pulse generated by heartbeat and which is coupled to such an interpreting unit to which is also coupled a measured signal indicating the measured value of the acting pressure, and that the interpreting unit is arranged to determine systolic pressure on the basis of such an acting pressure which is the pressure acting when the interpreting unit detects a change characteristic of systolic pressure in a pressure pulse signal measured by the sensor which measures the artery.
The method and measurement arrangement of the invention are based on the idea of using a sensor, which measures the pressure pulse and transfers its measurement data to the interpreting unit, to indicate from the measured acting pressure signal the points conforming with diastolic and/or systolic pressure.
The solution of the invention provides a plurality of advantages. The invention provides an extremely good measurement accuracy, allowing systolic and/or diastolic pressure to be determined extremely accurately, since their detection is based on a separate measurement of the pressure pulse, which is used to indicate the values of said systolic and/or diastolic pressures.